Why flying today isn't free.
      As kids didn't we all want to be airline pilots? What a job. You get up in the morning, jump into your plane and take your passengers on a wild trip to some cool destination. Flying free as a bird. Swooping over things that catch your eye. Exploring the world.
      Unfortunately that's not how it works. Pilots today pick from a very limited set of routes and altitudes. So they don't have very much more freedom than the captains on the submarines at Disneyland.

Flying direct with Free Flight
      Free Flight isn't any one thing. It isn't a single technology like radar that solves a specific problem. It's a coordinated set of technologies that will one day give airline pilots a lot more autonomy. Here's the big idea in a nutshell:

      Pick a route, any route! A pilot sitting on the runway in L.A. enters a destination, like Chicago, into the GPS navigation computer. It instantly calculates the great circle route to Chicago. The route is displayed on the cockpit terminal. Weather data from a national weather computer is overlaid on the display. The pilot decides to curve a little to the north to avoid a storm. The pilot takes off and starts flying along the path selected.

What is Free Flight?

      GPS guides the way. As the pilot flies, the GPS receiver continuously calculates the current position and displays the correct heading to Chicago. The pilot's position is also fed into a special data-link radio that transmits the data to a centralized computer on the ground. This computer sends the position to ground controllers and to any other planes in the area. These planes see the other planes on their displays.
      Computers watch for collisions. The pilot's on-board computer analyzes incoming data, looking for other planes. It maintains two imaginary perimeters around the plane. The widest boundary is an "alert" boundary. The size of this boundary depends on the speed and performance of the plane. If another plane's alert boundary intersects the pilot's alert boundary, the computer warns both pilots and the ground controllers. Together they take steps to move apart.
      Within the alert zone is a tighter boundary closer to the plane called the "protected" zone. The computers are programmed to never allow one's airplane to touch another's. That would mean the planes are dangerously close. The computers use direction and speed information to predict convergences long before they occur.
      Controllers are still involved. Free Flight is envisioned as a flexible system. The pilot's ability to act autonomously may be restricted in some situations, say as the plane nears a crowded airport or when weather forces many planes into the same area. The system would automatically pass authority from the pilot to controllers as the situation changes.
      It's ironic that to achieve the very simple goal of flying straight from A to B will require a very complex interplay of advanced technologies.
      Is it possible? Definitely. Look at the cellular phone system. A centralized computer must keep track of the location of millions of phones, switching the transmission of calls from cell to cell as your car moves along. All without breaking up a conversation. It's a very complicated system but it works everyday.

Benefits of Free Flight

Free flight will make a big difference in aviation for a variety of reasons:

Improved safety from better collision and weather avoidance
Lower fuel costs from shorter routes and more efficient terminal use
Shorter flights also from shorter routes and more efficient terminal use
Better air quality less fuel burned and spread over more space
Better overall airspace management spreads planes over more space and provides more      "visibility" of aircraft

What technology is needed?

     Free Flight will require lots of different technologies, but they can be roughly divided into three important groups: communication, navigation and surveillance.

Communication. For Free Flight to work, a system of voice and data communication with every plane must be established. The link must be very robust and capable of handling a lot of data. Right now the aeronautical radio frequencies are getting very crowded, so the ultimate system will probably need to be a modern digital system, perhaps involving satellites over oceans and wilderness. It will not only carry voice communication between pilots and ground controllers, but will also carry navigation data and weather information as well.

Navigation.The Global Positioning System is already the preferred navigation method for aviation. It's extremely accurate and available worldwide. To guarantee reliable data on a second-by- second basis the FAA is enhancing GPS with a system called the Wide Area Augmentation System (WAAS).

     WAAS improves on regular GPS by adding some extra geosynchronous satellites that transmit both GPS system condition messages and differential corrections to GPS receivers across the continent. This not only increases the accuracy of GPS to a level capable of Category 1 landings, but also guarantees that the GPS data reaching the planes is absolutely correct.

     This extremely precise position information is the key to Free Flight. If GPS says a plane is in a certain position we know it is in exactly that position. We don't have to build a fudge factor into airplane spacing to allow for slop in the position. In other words, we can space planes closer together without worrying about them colliding.

Surveillance. To be truly safe, the Free Flight system needs an automatic surveillance component too. This system would automatically warn a pilot of any approaching aircraft. It is envisioned that transponders on-board every aircraft would automatically transmit the planes exact position (as derived from GPS). These transmissions would be monitored by all other planes as well as by air traffic control. If the plane's on board computers receive a position that's within its "alert zone" an alarm warns the pilot. This system will rely on advanced radios and fault-tolerant computing.

Who's responsible for Free Flight?

     Free flight is being promoted by all arms of the aviation industry from the airlines and pilot associations to equipment manufacturers and the FAA itself. Most of the coordination and planning has been handled by the FAA and a private organization called RTCA that advises the FAA.
     RTCA is a consortium of industry and government experts who have been working to define the architecture of the Free Flight system and establish its specifications. Trimble's Military and Advanced Systems division participates on this committee and is actively contributing to the development of the technology.
     Most governments around the world are cooperating too. For many third-world countries, Free Flight represents a great opportunity to get modern air service without investing in the traditional infrastructure.
When will Free Flight be operational?

     Since Free Flight isn't a single entity it doesn't have a single "start" date. Different parts of the system will be phased-in as they become available. Work has already begun on many fronts.      Tests have been conducted in the United States and over the central Pacific. These tests demonstrated significant cost savings which should keep the industry's motivation high. A significant portion of the world's airlines should be flying free by 2010.